Method for manufacturing silver nanowires using ionic liquid

ABSTRACT

The present invention relates to a method of preparing silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more, and, more particularly, to a method of uniformly preparing silver nanowires having a high aspect ratio using an ionic liquid as an additive in addition to a silver salt precursor, a reducing solvent and a capping agent in a polyol process. When the technology of the present invention is used, silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more can be uniformly prepared. Further, when a transparent conductive film is formed by applying a silver nanowire-dispersed solution onto a base film, the transparent conductive film has a surface resistivity of 10 1 ˜10 3 Ω/□ and a light transmittance of 90% or more to the base film.

TECHNICAL FIELD

The present invention relates to a method of preparing silver nanowiresand, more particularly, to a method of uniformly preparing silvernanowires having an aspect ratio of 100 or more (for example, having adiameter of less than 100 nm and a length of 10 μm or more) using asilver salt precursor, a reducing solvent, a capping agent and an ionicliquid.

BACKGROUND ART

Recently, touch screen panels have been used as important components ofvarious types of electric, electronic and communication appliances, suchas smart phones, tablet computers, etc.

A transparent electrode film is used as a main component of a touchscreen panel. As the transparent electrode film, a film having a surfaceresistivity of 500Ω/□ and a light transmittance of 90% or more to a basefilm is used. Currently, indium tin oxide (ITO) is generally used as atransparent electrode material. A transparent electrode film having asurface resistivity of 50˜500Ω/□ and a light transmittance of 90% ormore to a base film can be fabricated by forming an ITO thin film on aglass substrate or a transparent polymer film using sputtering.

However, the ITO thin film is problematic in that its production cost isvery high and it is easily damaged due to the difference in thermalexpansibility or thermal shrinkability between the ITO thin film and abase film. Particularly, since the brittleness of the ITO thin filmformed on a polymer film is very high, when this ITO thin film is usedas a transparent electrode film of a touch screen panel, there is aproblem of the ITO thin film being cracked by mechanical or physicaldeformation.

Therefore, novel raw materials for transparent electrode films, whichcan overcome the above problems of ITO, have lately attractedconsiderable attention. For this purpose, there have been many effortsmade to fabricate a transparent electrode film using a novel rawmaterial such as a conducting polymer, a carbon nanotube, graphene or ametal nanowire. Particularly, metal nanowire, such as silver nanowire,has lately been in the spotlight as a transparent electrode materialthat can be used in place of ITO due to the metal wire having very highelectroconductvity and a high aspect ratio.

Silver nanowires, as reported in US 2005/0056118, Science 298, 2176,2002, Chem. Mater. 14, 4736, 2002, can be prepared by a so-called polyolprocess. Further, there is disclosed a method of synthesizing silvernanowires having a one-dimensional shape in a solution phase using asilver salt precursor (metal precursor), a reducing solvent such asethyleneglycol (EG) and a capping agent such as polyvinylpyrrolidone(PVP). Further, there was reported a method of synthesizing silvernanowires using an ionic liquid as a capping agent instead of PVP in thepolyol process (Angewandte Chemie, 121, 3864, 2009).

However, in such methods of synthesizing silver nanowires, differentshapes of silver nanoparticles as well as silver nanowires aresimultaneously prepared, so it is not suitable for using these silvernanoparticles as a transparent electrode material. For instance,granular silver nanostructures are prepared together with silvernanowires. In this case, there are problems in that granular silvernanostructures must be separated from silver nanostructures after thepreparation of silver nanostructures, and in that the yield of silvernanowires is low.

Further, Korean Unexamined Patent Application Publication No.10-2010-0055983 discloses a method of preparing metal nanowires by apolyol reduction reaction in which a metal salt is mixed and reactedwith a reducing solvent in the presence of an ionic liquid.

However, in order to fabricate a transparent electrode film havingexcellent light transmittance and surface resistance characteristicsusing silver nanowires, it is required to develop a method of moreuniformly synthesizing silver nanowires having a higher aspect ratio.

DISCLOSURE Technical Problem

An object of the present invention is to provide a technology ofuniformly and reproducibly preparing silver nanowires having an aspectratio of 100 or more (for example, having a diameter of less than 100 nmand a length of 10 μm or more) without preparing different shapes ofsilver nanostructures by a polyol reduction reaction using a metal saltas a precursor.

Other objects of the present invention are not limited to theabove-mentioned object, and will be clearly understood from thefollowing descriptions by those skilled in the art.

Technical Solution

The present invention relates to a method of preparing silver nanowireshaving a high aspect ratio (for example, having a diameter of less than100 nm and a length of 10 μm or more) using an imidazolium-based ionicliquid as an additive in a polyol process.

In order to accomplish the above object, silver nanowires were preparedby a polyol reaction in which an imidazolium-based ionic liquid(additive) was mixed and reacted with a mixed solution including asilver salt precursor, a reducing solvent and a capping agent.

From the research results of the present inventors, it was found that,in the process of preparing silver nanowires by the polyol reductionreaction of a mixed solution including a silver salt precursor (forexample, AgNO₃), a reducing solvent (for example, ethyleneglycol), acapping agent (for example, polyvinylpyrrolidone) and the like, when asmall amount of an imidazolium-based ionic liquid was added to the mixedsolution as an additive, silver nanowires having a diameter of less than100 nm and a length of 10 μm or more were uniformly prepared. The silversalt precursor is a compound including a silver cation and an organic orinorganic anion. For example, AgNO₃, AgClO₄, AgBF₄, AgPF₆, CH₃COOAg,AgCF₃SO₃, Ag₂SO₄, CH₃COCH═COCH₃Ag or the like may be used as the silversalt precursor. The silver salt is dissociated in a solvent, and is thenconverted into metal silver by a reduction reaction.

The reducing solvent is a polar solvent that can dissolve a silver salt.The reducing solvent is referred to as a solvent having two or morehydroxy groups in a molecule thereof, such as diol, polyol or glycol.Specific examples of the reducing solvent may include ethyleneglycol,1,2-propyleneglycol, 1,3-propyleneglycol, glycerin, glycerol,diethylglycol, and the like. The reducing solvent serves to producemetal silver by inducing the reduction reaction of silver cations at apredetermined temperature or more as well as serves as a solvent fordissolving a silver salt.

The capping agent serves to one-dimensionally grow silver nanoparticlesbecause it is adsorbed (hereinafter, capped) only on a specific crystalplane by the interaction between the capping agent and the silvernanoparticles formed in the initial stage of a synthesis reaction. Thecapping agent is polyvinylpyrrolidone (PVP) or polyvinylalcohol (PVA).

The imidazolium-based ionic liquid, as represented by Formulas 1 and 2below, is a monomeric or polymeric compound including an organic cationhaving an imidazolium group and an organic or inorganic anion.Particularly, in the case where the imidazolium-based ionic liquidincluding a chlorine ion (Cl⁻) or a bromine ion (Br⁻) as an anion isused as an additive, when a silver salt is converted into metal silverby a polyol reduction reaction, the metal silver nanoparticles areone-dimensionally and uniformly grown by the chemical interactionbetween the imidazolium-based ionic liquid and a silver ion or metalsilver, thus finally forming silver nanowires having a high aspectratio, that is, having a diameter of less than 100 nm and a length of 10μm or more.

In the present invention, the aspect ratio of silver nanowires is 100 ormore, but the upper limit thereof is not predetermined and can beadjusted to the maximum aspect ratio to such a degree that they canexist as silver nanowires by controlling the content of the ionicliquid. When the aspect ratio of silver nanowires is excessively large,they do not exist in the form of wire, and they may be entangled asyarn. Therefore, if necessary, uniform silver nanowires having a highaspect ratio can be prepared by controlling the content of the ionicliquid.

In the Formulas 1 and 2, R1, R2 and R3 are identical to or differentfrom each other, each of which is hydrogen or a hydrocarbon group of 1to 16 carbon atoms, and each of which includes at least one heteroatomselected from the group consisting of oxygen, sulfur, nitrogen,phosphorus, fluorine, chlorine, bromine, iodine and silicon. Further, X⁻is an anion, and is an organic or inorganic compound including a halogenion such as a chlorine ion (Cl⁻) or a bromine ion (Br⁻). n is arepetitive unit, and is a natural number.

Specific examples of the monomeric cationic compound represented byFormula 1 above may include 1,3-dimethylimidazolium,1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium (EMIM),1-butyl-3-methylimidazolium (BMIM), 1-hexyl-3-methylimidazolium (HMIM),1-octyl-3-methylimidazolium (OMIM), 1-decyl-3-methylimidazolium,1-dodecyl-3-methylimidazolium and 1-tetradecyl-3-imidazolium, andspecific examples of the polymeric cationic compound represented byFormula 2 above may include poly(1-vinyl-3-alkylimidazolium),poly(1-allyl-3-alkylimidazolium) andpoly(1-(meth)acryloyloxy-3-alkylimidazolium). In order to synthesizesilver nanowires, it is preferred that a chlorine ion (Cl⁻) or a bromineion (Br⁻) be used as the anion of the ionic liquid of Formula 1 or 2.

Hereinafter, the method of preparing silver nanowires according to thepresent invention will be described in detail.

First, a silver salt precursor, a reducing agent, a capping agent and anionic liquid are mixed at an appropriate ratio and then stirred at roomtemperature for a predetermined amount of time. Subsequently, themixture is reacted at a temperature of 50˜180° C. for 30 minutes˜7 daysto form silver nanowires. When the reaction temperature is low, reactiontime is long because it takes more time to grow silver nanowires, but onthe other hand, when the reaction temperature is high, silver nanowiresare formed relatively rapidly.

In the present invention, in order to uniformly prepare silvernanowires, the content ratio of each of the components of the mixture isimportant. It is preferred that the capping agent is included in anamount of 1 to 2 mol based on 1 mol of the silver salt precursor, andthe ionic liquid is included in an amount of 0.001 to 0.2 mol based on 1mol of the silver salt precursor. In this case, when the amount of thecapping agent is less than 1 mol and the amount of the ionic liquid isless than 0.001 mol, each of which being an excessively low amount,there is a problem in that silver nanowires are not uniformly formed andexist in a mixture of nanowires and nanoparticles. Further, when theamount of the capping agent is more than 2 mol and the amount of theionic liquid is more than 0.2 mol, each of which being an excessivelyhigh amount, there is a problem in that the diameter of silver nanowiresincreases to 100 nm or more, or three-dimensional silver nanoparticlesare formed, and thus it is difficult to form uniform silver nanowires.Particularly, when the ionic liquid is used in an amount of 0.005 to0.02 mol, it is advantageous to form uniform silver nanowires.

The silver nanowires formed in this way are filtered and then washedwith a solvent such as water or alcohol. These filtered silver nanowiresare dispersed in a solvent to prepare a silver nanowire-dispersedsolution. In this case, it is preferred that water or a water-basedsolvent be used as the solvent for dispersing the silver nanowires.Specific examples of the solvent for dispersing the silver nanowires mayinclude water, methanol, ethanol, n-propyl alcohol, iso-propyl alcohol,n-butanol, iso-butanol, hexanol, benzyl alcohol, diacetone alcohol,ethyleneglycol, propyleneglycol, glycerol, 1,4-dioxane, tetrahydrofuran(THF), ethyleneglycol monomethyl ether, ethylenglycol monoethyl ether,ethyleneglycol dimethyl ether, propyleneglycol monomethyl ether,propyleneglycol monoethyl ether, propyleneglycol dimethyl ether,N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide (DMA),acetonitrile, acetaldehyde, N-methyl-2-pyrrolidone, 2-pyrrolidone,N-vinyl-2-pyrrolidone, dimethylsulfoxide, n-butyrolactone, nitromethane,and ethyl lactate. These solvents may be used independently or in acombination thereof.

The silver nanowire-dispersed solution is prepared by dispersing 0.1˜5wt % of the silver nanowires of the present invention in 95˜99.9 wt % ofthe solvent. The silver nanowire-dispersed solution may further includea dispersant and a thickener in order to improve the dispersibility ofsilver nanowires.

Here, when the content of silver nanowires in the silvernanowire-dispersed solution is less than 0.1 wt %, there aredisadvantages in that surface resistivity becomes high because theamount of nanowires is excessively small, and in that coatabilitybecomes poor because wet-coating thickness must be increased. Further,when the content of silver nanowires in the silver nanowire-dispersedsolution is more than 5 wt %, there are disadvantages in that it isdifficult to coat the silver nanowire-dispersed solution because theamount of nanowires is excessively large, and in that lighttransmittance becomes low because an excessive amount of silvernanowires is used.

The dispersant serves to allow silver nanowires to be stably dispersedin a solvent by electrostatic repulsion or steric barrier because thedispersant is adsorbed on the surface of silver nanowires. The thickenerserves to adjust the fluidity of the silver nanowire-dispersed solution.It is effective that each of the dispersant and the thickener beincluded in an amount of 0.01 to 10 parts by weight based on 100 partsby weight of the silver nanowire-dispersed solution. Here, when theamount of the dispersant is less than 0.01 wt %, there is a disadvantagein that a dispersion effect is barely exhibited. Further, when theamount thereof is more than 10 wt %, there is a disadvantage in that theamount of the dispersant is excessively large, and thus this dispersantleak out from the surface of the silver nanowire-dispersed solution todecrease the surface resistivity thereof or the surface thereof becomesexcessively slippery.

The dispersant may include at least one selected from the groupconsisting of polyoxyethylene aliphatic ether, polyoxyethylene phenylether, polyimine, alkyl phosphate, an alkylammonium salt, a polyesteralkylolammonium salt, a polyacrylic alkylolammonium salt,polydimethylsilane, polyacrylic acid, polysulfonic acid andpolyvinylpyrrolidone. More specifically, the dispersant may include atleast one selected from the group consisting of Triton X-100, TritonX-200, Pluronic P123, F127, F68, L64, BYK-181, 184, 191, 192, 194,Disperbyk-181, 184, 190, Tego 710, 720W, 730W, Zonyl FSN, FSO, FSP,cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride(CTAC), tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride(TBAC), sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate(SDBS), polystyrene sulfonate (PSSA), poly(sodium-4-styrenesulfonate)(PSSNa), and dodecylbenzenesulfonate (DBSA). Examples of the thickenermay include, but are not limited to, a urethane-modified thickener, anacrylic thickener, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcelluloseand hydroxypropylmethylcellulose. These thickeners may be usedindependently or in a combination thereof.

When the silver nanowire-dispersed solution including the silvernanowires prepared by the technology of the present invention is appliedonto a base film and then dried, a transparent electrode film includinga three-dimensional network formed of silver nanowires having a diameterof less than 100 nm and a length of 10 μm or more can be manufactured.

The base film may be a commonly-used transparent film, but is notlimited thereto. For example, the base film may be formed ofpolyethylene terephthalate, polyester naphthalate, polycarbonate,polymethylmethacrylate, polyacrylate, polyacrylonitrile, polystyrene orthe like. Meanwhile, in order to improve the adhesivity between the basefilm and the silver nanowires, an adhesion enhancing layer may beapplied to the surface of the base film or the base film may besurface-treated by corona treatment, plasma treatment or the like.

As the method of coating a base film with silver nanowires, allcommonly-known technologies may be used. General examples of the coatingmethod may include, but are not limited to, dip coating, spin coating,bar coating, gravure printing, reverse gravure printing, offsetprinting, ink-jet printing, spray coating and slot die coating.

The transparent electrode film made of the silver nanowires has asurface resistivity of 10¹˜10³Ω/□ and a light transmittance of 90% ormore to the base film.

Advantageous Effects

When the technology of the present invention is used, silver nanowireshaving a diameter of less than 100 nm and a length of 10 μm or more canbe uniformly prepared in a solution phase. Further, since each of thesilver nanowires of the present invention has a large aspect ratio of100 or more, when a three-dimensional network is formed on the surfaceof a base film using the silver nanowires, low surface resistivity andhigh light transmittance can be simultaneously realized.

DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 are scanning electron microscope photographs showing thesilver nanowires and silver nanoparticles of Comparative Example 1,respectively.

FIG. 3 is an electron microscope photograph showing the silver nanowiresof Example 1.

FIG. 4 is an electron microscope photograph showing the silver nanowiresof Example 2.

FIG. 5 is an electron microscope photograph showing the silver nanowiresof Example 3.

FIG. 6 is an electron microscope photograph showing the silvernanoparticles of Comparative Example 2.

MODE FOR INVENTION

Hereinafter, the present invention will be described in more detail withreference to the following Examples. However, these Examples are setforth to illustrate the present invention, and the scope of the presentinvention is not limited thereto.

Comparative Example 1 Preparation of Silver Nanowires Using PolyolReaction

0.1 mol (17 g) of AgNO₃ (manufactured by Kojima Co., Ltd., purity:99.99%) and 0.15 mol (16.7 g) of PVP (manufactured by AldrichCorporation, weight average molecular weight: 55,000 g/mol) were putinto a 2 L round-bottom flask, dissolved in 1 L of ethyleneglycol (EG),and then stirred at room temperature for 10 minutes to obtain atransparent mixed solution. The color of the mixed solution became graybrown as soon as the mixed solution was reacted at 150° C. for about 30minutes. Subsequently, the mixed solution was cooled to roomtemperature, filtered by a filter having a pore size of 1 μm, dried, andthen observed using a scanning electron microscope. As shown in thephotographs of FIGS. 1 and 2, it was observed that silver nanowireshaving a diameter of 90˜120 nm and a length of 5˜20 μm were formed, butthe diameters of the silver nanowires were somewhat large and notuniform. Further, it was observed that silver nanoparticles having aparticle size of 0.5˜5 μm were formed together with the silvernanowires.

Example 1 Preparation of Silver Nanowires Using Ionic Liquid ContainingChlorine Ion (Cl⁻) as Additive in Polyol Reaction

0.1 mol of AgNO₃, 0.15 mol of PVP and 0.001 mol of1-ethyl-3-methylimidazolium chloride (EMIM-Cl) were dissolved in 1 L ofethyleneglycol (EG), and were then stirred at room temperature for 10minutes to obtain a transparent mixed solution. The color of the mixedsolution became gray as soon as the mixed solution was reacted at 150°C. for about 30 minutes. Subsequently, the mixed solution was cooled toroom temperature, filtered by a filter having a pore size of 1 μm,dried, and then observed using a scanning electron microscope. As shownin the photograph of FIG. 3, it was observed that silver nanowireshaving a diameter of 55˜65 nm and a length of 10˜30 μm were uniformlyformed. Further, it was observed that, differently from the results ofComparative Example 1 in which an ionic liquid was not used, silvernanoparticles having different shapes from the silver nanowires were notdiscovered.

Example 2 Preparation of Silver Nanowires Using Ionic Liquid ContainingChlorine Ion (Cl⁻) as Additive in Polyol Reaction

Example 2 is the same as Example 1, except that 0.001 mol of1-butyl-3-methylimidazolium chloride (BMIM-Cl) was used as an ionicliquid. As shown in the photograph of FIG. 4, it was observed thatsilver nanowires having a diameter of 55˜65 nm were uniformly formed.Further, it was observed that, similarly to the results of Example 1,silver nanoparticles having different shapes from the silver nanowireswere not discovered. Comparing the results of Example 2 with the resultsof Example 1, it was observed that the shapes of silver nanowires werenot changed or were only slightly changed depending on the length of analkyl group of an imidazolium-based ionic liquid having a cation.

Example 3 Preparation of Silver Nanowires Using Ionic Liquid ContainingBromine Ion (Br⁻) as Additive in Polyol Reaction

Example 3 is the same as Example 2, except that 0.001 mol of1-butyl-3-methylimidazolium bromide (BMIM-Br) was used as an ionicliquid. As shown in the photograph of FIG. 5, it was observed thatsilver nanowires having a diameter of about 30 nm were uniformly formed.Further, it was observed that, similarly to the results of Example 1,silver nanoparticles having different shapes from the silver nanowireswere not discovered. Comparing the results of Example 3 with the resultsof Example 2, it was observed that the shapes and diameters of silvernanowires were changed depending on the anion of the ionic liquid.

Comparative Example 2 Preparation of Silver Nanowires Using Ionic LiquidContaining Bromine Ion (Br⁻) as Additive in Polyol Reaction

Comparative Example 2 is the same as Example 2, except that1-butyl-3-methylimidazolium methyl sulfate (BMIM-MeSO₄) was used as anionic liquid. When the anion of an ionic liquid was Cl— or Br— as inExamples 2 and 3, silver nanowires were formed. In contrast, when theanion of an ionic liquid was CH₃SO₄ ⁻ as in Comparative Example 2, asshown in the photograph of FIG. 6, it can be ascertained thatthree-dimensional silver nanoparticles, not one-dimensional silvernanowires, were formed.

Example 4 Manufacture of Transparent Conductive Film Using SilverNanowires Having High Aspect Ratio

0.7 parts by weight of the silver nanowires prepared in Example 2, 98.8parts by weight of iso-propyl alcohol and 0.5 parts by weight of acellulose-based thickener were mixed, and were then ultrasonicallydispersed to prepare a silver nanowire-dispersed solution. Subsequently,the silver nanowire-dispersed solution was applied onto a polyethyleneterephthalate film (thickness: 125 μm) coated with an acrylic adhesionenhancing layer using a bar coater, and was then dried at a temperatureof about 100° C. for 1 minute to form a transparent conductive film. Thesurface resistivity of the transparent conductive film was measuredusing a four-probe method (AIT Corporation). As a result, the surfaceresistivity thereof was about 95Ω/□. Further, the light transmittance ofthe transparent conductive film was measured using a UV-Vis-NIRspectrophotometer (Cary 5000). As a result, the light transmittance ofthe transparent conductive film to the base film was 94.7%.

INDUSTRIAL APPLICABILITY

The silver nanowires can be used as a main raw material of a touchscreen panel which is an important component of various types ofelectric, electronic and communication appliances, such as smart phones,tablet computers, televisions, etc.

1. A method of preparing silver nanowires by a polyol reduction reactionof a mixed solution including a silver salt precursor, a reducingsolvent and a capping agent, wherein the polyol reduction reaction ofthe mixed solution is performed by adding an ionic liquid to the mixedsolution as an additive, wherein the ionic liquid is a compoundcomprising an organic cation having an imidazolium group and an organicor inorganic anion, the compound being represented by Formula 1 below inthe form of a monomer or being represented by Formula 2 below in theform of a polymer:

where R1, R2 and R3 are identical to or different from each other, eachof which is hydrogen or a hydrocarbon group of 1 to 16 carbon atoms, andeach of which includes at least one heteroatom selected from the groupconsisting of oxygen, sulfur, nitrogen, phosphorus, fluorine, chlorine,bromine, iodine and silicon; X— is an anion, and is an organic orinorganic compound including a halogen ion such as a chlorine ion (Cl⁻)or a bromine ion (Br⁻); and n is a repetitive unit, and is a naturalnumber.
 2. (canceled)
 3. The method of claim 1, wherein, in the ionicliquid, the monomeric cationic compound is selected from the groupconsisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium,1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium,1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium,1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium and1-tetradecyl-3-imidazolium, and the polymeric cationic compound isselected from the group consisting of poly(1-vinyl-3-alkylimidazolium),poly(1-allyl-3-alkylimidazolium) andpoly(1-(meth)acryloyloxy-3-alkylimidazolium).
 4. The method of claim 3,wherein, in a mixing ratio of a silver salt precursor, a capping agentand an ionic liquid, the capping agent is included in an amount of 1 to2 mol based on 1 mol of the silver salt precursor, and the ionic liquidis included in an amount of 0.001 to 0.2 mol based on 1 mol of thesilver salt precursor.
 5. The method of claim 4, wherein a reactiontemperature for synthesizing silver nanowires is 50˜180° C.
 6. Themethod of claim 5 wherein the silver salt precursor includes a silvercation and an organic or inorganic anion, and includes at least oneselected from the group consisting of AgNO₃, AgClO₄, AgBF₄, AgPF₆,CH₃COOAg, AgCF₃SO₃, Ag₂SO₄, CH₃COCH═COCH₃Ag.
 7. The method of claim 1,wherein the reducing solvent is a solvent including diol, polyol orglycol having two or more hydroxy groups in a molecule thereof.
 8. Themethod of claim 5, wherein the capping agent is polyvinylpyrrolidone(PVP) or polyvinylalcohol (PVA).
 9. (canceled)
 10. A silvernanowire-dispersed solution prepared by dispersing 0.1˜5 wt % of thesilver nanowires having an aspect ratio of 100 or more, prepared by themethod of claim 1 in 95˜99.9 wt % of a solvent.
 11. The silvernanowire-dispersed solution of claim 10, wherein the solvent includes atleast one selected from the group consisting of water, methanol,ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, iso-butanol,hexanol, benzyl alcohol, diacetone alcohol, ethyleneglycol,propyleneglycol, glycerol, 1,4-dioxane, tetrahydrofuran (THF),ethyleneglycol monomethyl ether, ethylenglycol monoethyl ether,ethyleneglycol dimethyl ether, propyleneglycol monomethyl ether,propyleneglycol monoethyl ether, propyleneglycol dimethyl ether,N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide (DMA),acetonitrile, acetaldehyde, N-methyl-2-pyrrolidone, 2-pyrrolidone,N-vinyl-2-pyrrolidone, dimethylsulfoxide, n-butyrolactone, nitromethane,and ethyl lactate.
 12. The silver nanowire-dispersed solution of claim11, further comprising 0.01 to 10 parts by weight of a dispersant and0.01 to 10 parts by weight of a thickener based on 100 parts by weightof the silver nanowire-dispersed solution.
 13. The silvernanowire-dispersed solution of claim 12, wherein the dispersant includesat least one selected from the group consisting of polyoxyethylenealiphatic ether, polyoxyethylene phenyl ether, polyimine, alkylphosphate, an alkylammonium salt, a polyester alkylolammonium salt, apolyacrylic alkylolammonium salt, polydimethylsilane, polyacrylic acid,polysulfonic acid and polyvinylpyrrolidone, and the thickener includesat least one selected from the group consisting of a urethane-modifiedthickener, an acrylic thickener, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcelluloseand hydroxypropylmethylcellulose.
 14. A transparent conductive filmformed by applying the silver nanowire-dispersed solution including thesilver nanowires prepared by the method of claim 1 onto a base film. 15.The transparent conductive film of claim 14, wherein the transparentconductive film has a surface resistivity of 10¹˜10Ω/□ and a lighttransmittance of 90% or more to the base film.
 16. The method of claim3, wherein the reducing solvent is a solvent including diol, polyol orglycol having two or more hydroxy groups in a molecule thereof.
 17. Themethod of claim 4, wherein the reducing solvent is a solvent includingdiol, polyol or glycol having two or more hydroxy groups in a moleculethereof.
 18. The method of claim 5, wherein the reducing solvent is asolvent including diol, polyol or glycol having two or more hydroxygroups in a molecule thereof.
 19. The method of claim 6, wherein thereducing solvent is a solvent including diol, polyol or glycol havingtwo or more hydroxy groups in a molecule thereof.
 20. A silvernanowire-dispersed solution prepared by dispersing 0.1˜5 wt % of thesilver nanowires having an aspect ratio of 100 or more, prepared by themethod of claim 7 in 95˜99.9 wt % of a solvent.
 21. The silvernanowire-dispersed solution of claim 20, further comprising 0.01 to 10parts by weight of a dispersant and 0.01 to 10 parts by weight of athickener based on 100 parts by weight of the silver nanowire-dispersedsolution.
 22. The silver nanowire-dispersed solution of claim 21,wherein the dispersant includes at least one selected from the groupconsisting of polyoxyethylene aliphatic ether, polyoxyethylene phenylether, polyimine, alkyl phosphate, an alkylammonium salt, a polyesteralkylolammonium salt, a polyacrylic alkylolammonium salt,polydimethylsilane, polyacrylic acid, polysulfonic acid andpolyvinylpyrrolidone, and the thickener includes at least one selectedfrom the group consisting of a urethane-modified thickener, an acrylicthickener, methylcellulose, ethylcellulose, hydroxyethylcellulose,hydroxymethylcellulose, hydroxypropylcellulose andhydroxypropylmethylcellulose.